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What are classification keys?

Part of ScienceLiving things and their habitatsYear 4

Classification keys

A young girl standing by a pond comparing a frog and a toad

Classification helps scientists to put living things into groups based on things that make them the same.

To identify the things that are the same and different when comparing living things, we can use a classification key, which is a set of questions about the characteristics of living things.

The answer to the first question branches off to give you another question to answer, and so on. As you answer more questions you narrow down your choices until the last question tells you what your living thing is.

A young girl standing by a pond comparing a frog and a toad
An example of a classification key showing invertebrates with soft and hard bodies
An example of a classification key
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Watch: What are classification keys?

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Watch: How to classify animals

Let's separate these amphibians into two football teams.

Fascinating facts

An illustration of a killer whale
A killer whale
  • There are over 2.16 million known animal species.
  • All whales, like killer whales, are mammals, the same as humans. Despite living in the sea they need to breathe oxygen from the air.
  • Today there are about 1 million known species, or types, of insect.
  • Grouping animals according to the characteristics that are similar doesn’t always mean that you group them correctly – a bat, a dragonfly and a duck all have wings and can fly but belong to different animal groups.
  • The Etruscan shrew is the lightest and smallest mammal, weighing as little as 1.5g, about the same as half a teaspoon of sugar!
  • Invertebrates make up around 97% of all the animal species on Earth.
  • The largest animals in the main ecosystems are vertebrates.
An illustration of a killer whale
A killer whale
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Slideshow: What is classification?

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  1. An eagle flying in Scotland, UK.

    Classification

    Animals are divided into two main groups, invertebrates and invertebrates. Animals like this golden eagle that have a backbone (spine) are called vertebrates.

A bear in a river with salmon in its mouth.
A bear in a river with salmon in its mouth.

Did you know?

Classification keys can ask questions about a variety of characteristics of living things such as:

  • What it looks like
  • The climate that it lives in-The type of habitat you might find it in
  • What it eats or how it breathes.
A bear in a river with salmon in its mouth.
A bear in a river with salmon in its mouth.
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Watch: Using a classification key

Find out the how to identify and classify this mystery creature using a classification key.

A cat and a dog
A domestic cat and dog

Did you know?

The branch of science that classifies living things is called taxonomy.

The classification system was first developed by the Swedish scientist Carl Linnaeus. He gave each organism a two part Latin scientific name.

His system is now used all across the world. Humans are Homo sapiens; a house cat would be Felis catus.

A cat and a dog
A domestic cat and dog
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Important words

An illustration of a blue dart frog
A poison dart frog is a vertebrate because it has a backbone

Classification – Placing living things into groups based on characteristics they have that are the same.

Classification key – A set of questions about the characteristics of living things.

Invertebrates – Animals that don't have a backbone.

Taxonomy – The branch of science that classifies living things.

Vertebrates – Animals that have a backbone (spine).

An illustration of a blue dart frog
A poison dart frog is a vertebrate because it has a backbone
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Activities

Activity 1 – Frog or toad?

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Activity 2 – Classify the animals

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Activity 3 – Classification keys quiz

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Activity 4 – Create a classification key

Can you create your own classification key?

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